Screw cap

ABSTRACT

The present invention relates to a screw cap ( 1 ) having a disk-shaped top part and having a flange edge an internal thread, which adjoins the outer circumference and extending perpendicular to the top part, wherein a bung opening with a bung plug ( 3 ) with an automatic venting device is arranged in midsection of the top part of the screw cap ( 1 ), as a result of which air can flow into the inner plastic container ( 11 ) of a pallet container ( 10 ), to prevent the collapse of the thin-walled inner plastic container ( 11 ) when liquid content is withdrawn from the inner container ( 11 ) while the discharge fitting ( 14 ) is open. A core element of the venting device is a disk-shaped valve disk ( 5 ) which is made of plastic and provided as a sealing element with a resilient element ( 6 ) that is also made of plastic, wherein the resilient element ( 6 ) is located below the valve disk ( 5 ) and has at least three elastic spring legs ( 20 ) which are shaped as ribs and arranged on its outer edge of the resilient element forming segments of a circle.

The invention relates to a screw cap with a disk-shaped top part and a flange edge with an inner thread adjoining the outer circumference and extending perpendicular to the top part, wherein a bung opening with a bung plug having an automatic venting device is inserted in the center of the top part of the screw cap. Such screw caps are typically used for closing the upper fill opening of large volume pallet containers that have a fill volume of, e.g., 1000 liter.

STATE OF THE ART

Large-volume pallet containers are increasingly used for storing and transporting hazardous liquid contents (like e.g., chemicals). These pallet containers have an inner plastic container which is placed on a bottom pallet and a support jacket which is made of a tubular cage which closely surrounds the inner container and is secured to the bottom pallet. A corresponding screw cap (typical having a nominal width of 150 mm, 240 mm or larger) is used for closing the fill opening located in the top of the inner container. The fill opening in the top of the inner plastic container has a raised flange edge with an outside thread, onto which the screw cap is screwed, with an interposed seal providing gas- and liquid-tightness.

For example, EP-B 0 858 955 discloses a particular screw cap with an automatic venting device for use with pallet containers. In this conventional embodiment, the venting device is housed in a bung plug that is screwed in. The sealing element is here a thin membrane disk made of rubber or plastic which is formed so as to yield elastically due to its low material-specific stiffness in response to a reduced pressure in the container, with its thin outside edge admitting air into the container interior.

However, with this embodiment, the diminishing elasticity of the thin membrane disk over time is disadvantageous. The membrane disk must also be protected from upwardly splashing fill material by a splash guard, because otherwise the membrane disk would be at great risk to adhere to the bung plug, thus preventing the intended admission of air.

PROBLEM

When dispensing hot, slowly cooling contents, but in particular when rapidly withdrawing liquid content from the lower discharge fitting, a reduced pressure is disadvantageously generated in the container of large-volume pallet containers, so that the thin-wall inner plastic container collapses, unless countermeasures are taken. Typically, when fully discharging the liquid content, the screw cap is simply manually unscrewed or loosened from the fill opening by an operator, until a volume of air equal to the volume of the discharged liquid can enter the interior of the plastic container. However, an operator oftentimes forgets to loosen the screw cap before withdrawing the liquid or to close the screw cap after the liquid content has been withdrawn. In particular in automated production processes, which involve storage of liquid components in pallet containers and sequentially supply to the production process, the screw cap can no longer be operated by hand, so that screw caps with automatic venting devices must be employed.

It is an object of the present invention to provide a screw cap or bung plug with automatic venting device, in particular for large containers such as pallet containers, to prevent generation of an undesirable reduced pressure inside the container, and hence to reliably prevent the container from collapsing. The screw cap or bung plug with an automatic venting device should have simple design and should be easy to manufacture at low cost and resist adhesion due to splattered content.

The object is attained by the invention the features set forth in claim 1. Additional advantageous embodiments of the present invention are recited in the dependent claims.

According to the invention, a core component of the venting device is a disk-shape valve disk made of plastic, with a separate resilient element also made of plastic, wherein the resilient element is arranged below the valve disk and has at least three elastic spring legs. The installation of the prefabricated injection molded plastic parts in the screw cap or bung plug is relatively simple and cost-effective, with the separate resilient element ensuring that the valve disk opens and closes reliably. The bung plug has a through opening for air with a diameter of about 20 mm (±2 mm), allowing unimpeded airflow of up to 200 l/min. This approach effectively prevents the thin-walled inner plastic container from imploding or collapsing, when the liquid content is withdrawn. The venting device can therefore prevent reduced pressure in the container from causing undesirable indentations in the container wall or depressions in the top of the thin-walled inner plastic container. The ventilation opening allows proportionate admission of air in the screw cap of the fill opening and a steady outflow without undesirable gurgling and without detrimental generation of a reduced pressure in the container interior, when content is withdrawn from the lower withdrawal fitting of a pallet container.

The present invention is characterized more particularly by the following features:

-   -   the air passage has a large diameter of about 20 mm,     -   the air passage allows unimpeded airflow of up to 200 l/min,     -   the sealing disk implemented as a valve disk has a diameter of         about 28 mm (±2 mm),     -   the valve disk as well as the bung plug/screw cap are made of         HD-PE,     -   the valve disk is urged against the vent opening by a separate         resilient element having three or four spring legs,     -   the spring legs engage in a stabilizing manner on the outer edge         of the resilient element or are attached to the outer edge of         the resilient element,     -   the spring legs of the resilient element are in the form of         spring ribs having a rectangular cross-section and extending         along a partial circle,     -   the spring legs are supported on the outside against an inner         ring flange of an adapter ring in the bung plug on a large         diameter,     -   the resilient element, valve disk and adapter ring are made of         HD-PE,     -   the resilient element, valve disk and adapter ring are         fabricated as low-cost injection molded parts,     -   the valve disk opens automatically, when a reduced pressure is         applied, and closes due to the spring force of the resilient         element and/or the return force of the elastic spring legs, when         the reduced pressure is removed.

According to a preferred embodiment of the invention, the venting device is implemented as a conventional two-inch bung plug (70×6) with an outside diameter of about 70 mm.

An exemplary embodiment of the invention will now be described in more detail with reference to the drawings, which show in:

FIG. 1 a screw cap with venting device in accordance with the invention,

FIG. 2 a side view of a pallet container,

FIG. 3 an exploded view of the screw cap according to FIG. 1,

FIG. 4 a bung plug for use in the venting device,

FIG. 5 the valve disk of the venting device by way of perspective and cross-sectional views,

FIG. 6 a resilient element of the venting device by way of perspective and cross-sectional views,

FIG. 7 an adapter ring of the venting device by way of perspective and cross-sectional views,

FIG. 8 a cover with a seal of originality,

FIG. 9 a cap for the sealing cover,

FIG. 10 the bung plug with venting device in a closed state, and

FIG. 11 the bung plug with venting device in an open state.

FIG. 1 shows the screw cap 1 according to the invention with automatic venting device. The screw cap 1 has a disk-shaped top part and a flange edge which extends perpendicular to the top part and has an inner thread located at its outer circumference. A sealing ring 2 is inserted in the flange edge above the thread. The screw cap 1 according to the invention is used for closing the fill opening of typical pallet containers. The inner plastic containers have in the top an upwardly pointing flange edge with an outer thread, on which the screw cap 1 with the venting device is firmly screwed.

A bung fitting opening is arranged in a bung fitting with an inner thread in midsection in the disk-shaped top part of the screw cap 1 for threaded engagement of a bung plug 3 with a venting device in a gas- and liquid-tight manner by means of another sealing ring 4. The actual venting device is made of three separate parts, namely a valve disk 5, a resilient element 6 and an adapter ring 7. A cover 8 with a seal is placed on the outside of the bung plug fitting to guarantee authenticity, which is in turn covered by a cap 9 to protect against ingress of rainwater, when the pallet container is stored outside.

FIG. 2 illustrates with the reference numeral 10 a pallet container for storing and transporting, in particular, hazardous liquid contents. The pallet container is essentially constructed of three components, namely a thin-walled inner container 11 made of a thermoplastic material, a lattice framework 12 closely surrounding the inner plastic container 11 as a support jacket, and a bottom pallet 13 on which the lattice framework 12 is secured. The inner plastic container 11 has a fill opening, which is arranged in the top and can be closed with a screw cap, and a discharge opening with a discharge fitting 14 for the liquid contents in a side in midsection of the top is closed with a screw cap 1 (type DN 150), as shown in FIG. 1. FIG. 3 shows a more detailed side view (exploded view) of the screw cap 1, with the venting device constructed as a one-way valve.

The large sealing ring 2 seals the screwed-on screw cap 1 in the closed state against the upper end face of the flange edge in the top of the inner plastic container of the pallet container. The bung plug 3 is screwed by way of the smaller sealing ring 4 into the bung opening in the bung fitting with inner thread in midsection of the screw cap 1. The venting device, comprised of the separate components valve disk 5, resilient element 6, and adapter ring 7, is inserted into the bung plug 3 from below. The bung plug 3 is covered on the outside or from atop, respectively, by means of the cover 8 with seal of authenticity and the cap 9.

The bung plug 3 depicted in FIG. 4 by way of a perspective view is a conventional two-inch bung plug with an outside diameter of about 70 mm, has in midsection an opening 15 for unimpeded passage of air. The air passage opening 15 has a diameter of about 20 mm. Special bung plug configurations are always required for other conventional bung plugs with a venting device. The bung plug 3 according to the present invention, however, can be used with a vent button inserted into the central opening or a blind plug operating as a vent closure or as a conventional gas-tight bung plug closure.

FIG. 5 shows the valve disk 5 in both a perspective view and a cross-sectional view. The valve disk 5 has a sealing edge 16 which slopes upwardly and thins out towards the outside, with a solid base ring 17 located below. The valve disk 5 has in midsection a large opening of about 20 mm for passage of air and is configured similar to a valve disk ring. The resilient element 6 of the venting device has an overall diameter of about 40 mm and is depicted in FIG. 6 by way of a perspective view and a cross-sectional view on an enlarged scale. The resilient element 6 includes an upwardly pointing ring flange 18 with a diameter of about 20 mm, a disk-shaped section 19, and three spring legs or spring ribs 20 arranged on the outer edge of the disk-shaped section 19. The spring legs 20 are formed as segments of a circle, i.e., they extend over a partial circle of the disk-shaped section 19 between about 85° and 120° and have a rectangular cross-section with an edge length of about 1 mm to 2 mm, preferably of about 1.2×1.2 mm. In another embodiment, the valve disk 5 and the resilient element 6 are fabricated by injection molding as a contiguous one-piece integral component, which further reduces the part count.

When constructed as separate parts, the valve disk 5 can be made of an elastically softer plastic material (HD-PE) and the resilience element 6 of a harder or stiffer plastic material (HD-PE) with a greater spring return characteristic.

FIG. 7 illustrates the adapter ring 7 by way of a perspective view and a cross-sectional view. The adapter ring 7 includes essentially of an annular body 21 and an inner radial flange ring 22. The venting device is installed by first pressing the valve disk 5 on the ring flange 18 of the resilient element 6. The resilient element 6 with the attached valve disk 5 is then loosely inserted from above in the adapter ring 7. The adapter ring 7 with the inserted resilient element 6 and the valve disk 5 are then inserted into the bung plug 3 from below and permanently pressed into the ring flange 23 of the bung plug 3. The ring flange 23 of the bung plug 3 and the adapter ring 7 virtually form a cage for receiving the automatic venting device. The valve disk 5 with the resilient element 6 is inserted into the cage formed on the bottom side of the bung plug 3 from the ring flange 23 and the adapter ring 7 and freely movable therein. The valve disk 5 is elastically supported from above by the bung plug 3, whereas the resilient element 6 is elastically supported in the radial direction by the lower end of its spring legs 20 against the radial flange ring 22 which protrudes radially inwardly on the inside of the adapter ring 7.

For a permanent and non-releasable connection, the inside of the ring flange 23 of the bung plug and the outside of the adapter ring 7 are provided with a longitudinal and/or transverse groove profile 24. The adapter ring 7 can also be affixed in the ring flange 23 of the bung plug 3 with an adhesive or welded by ultrasonic welding.

All components of the bung plug with a venting device have a comparatively simple construction and can be easily installed together; they are made essentially of a thermoplastic material HD-PE (High Density Poly Ethylene) and can be recycled and reused without requiring further separation or sorting.

FIG. 8 shows a particular embodiment of a cover 8 with a seal implemented as an originality seal with a tear-off strip. The cover 8 with the seal has a plurality of small vent openings 25 which ensure unimpeded and adequate air supply. To prevent rain water from entering the container interior when filled pallet containers are stored outside, a simple cap 9 is placed on the cover 8 with the seal. The cap 9 illustrated in FIG. 9 includes several holding tabs 26 which ensure a secure seat on the cover 8 with the seal.

To illustrate the operation, FIG. 10 shows the bung plug 3 of the screw cap 1 of the invention with an automatic venting device in a closed state. As long as there is no reduced pressure in the container interior, the valve disk 5 sealingly contacts the bottom side of the housing disk in the bung plug 3. The valve disk 5 opens to allow air to enter the inner container only when liquid bulk material is withdrawn from the pallet container 10, with the discharge fitting 14 in the open position, and a certain reduced pressure is generated in the container interior. FIG. 11 shows the bung plug 3 with an automatic venting device in an open state. Depending on the prevailing reduced pressure, the valve disk 5 is more or less spaced from the bottom side of the housing disk in the bung plug 3.

The bung plug 3 has for the venting device an unobstructed air passage opening 15 (without interfering cross brace) with a diameter of about 20 mm (±2 mm), allowing sufficient airflow of up to 200 l/min. The air passage opening 15 can be closed with a valve disk forming a sealing element and placed on the resilient element. The central opening of the valve disk 5 is firmly pressed onto the ring flange 18 (diameter abroad 20 mm) of the resilient element 6. The valve disk, resilient element, adapter ring and bung plug or screw cap are made of HD-PE plastic. The valve disk is urged in front of the air passage opening in the bung plug by three or four spring legs secured on the outer edge of the resilient element. The spring legs are formed as ribs on a partial circle and are supported on the outside against a radial ring flange of the screw cap or the adapter ring on a large diameter of about 40 mm. For a cost-effective solution, the valve disk with the integrated resilient element is made of a separate prefabricated HD-PE injection molded part. The valve disk automatically opens under a reduced pressure and closes automatically when the reduced pressure is removed, due to the spring force of the resilient element and/or the return force of the three spring legs.

LIST OF REFERENCE SYMBOLS

-   1 screw cap -   2 sealing ring (1) -   3 bung plug -   4 sealing ring (4) -   5 valve disk -   6 resilient element -   7 adapter ring -   8 cover with a seal -   9 cap -   10 pallet container -   11 inner plastic container -   12 lattice frame -   13 bottom pallet -   14 discharge fitting (11) -   15 air passage opening (3) -   16 sealing edge (5) -   17 base ring (5) -   18 ring flange (6) -   19 disk-shaped part (6) -   20 spring legs/ribs (6) -   21 annular body (7) -   22 radial flange ring (7) -   23 ring flange (3) -   24 groove profile (7) -   25 ventilation openings/bores (8) -   26 holding taps (9) 

1.-11. (canceled)
 12. A screw cap for a container, comprising a disk-shaped top part having a bung opening, a flange edge extending perpendicular from an outer periphery of the disk-shaped top part and having an inner thread, and a bung plug having an automatic venting device disposed in the bung opening, the automatic venting device comprising a sealing element configured as a disk-shaped valve disk made of plastic and a resilient element also made of plastic, with the resilient element facing away from the valve disk and comprising at least three elastic spring legs, wherein the automatic venting device allows air to enter the container when a withdrawal fitting of the container is open and liquid bulk material is withdrawn from the container.
 13. The screw cap of claim 12, wherein the spring legs are formed as ribs and are arranged on an outer edge of the resilient element so as to form segments of a circle.
 14. The screw cap of claim 13, wherein the spring legs have a rectangular cross-section with an edge length of about 1 to 2 mm.
 15. The screw cap of claim 12, wherein the valve disk and the resilient element are made as a single contiguous component from HDPE plastic by injection molding.
 16. The screw cap of claim 12, wherein the valve disk and the resilient element are made as two separate components by injection molding.
 17. The screw cap of claim 16, wherein the valve disk is made of a plastic material (HD-PE) which is softer than a plastic material (HD-PE) of the resilient element.
 18. The screw cap of claim 12, wherein the bung plug has a bottom side with a ring flange and an adapter ring permanently inserted in the ring flange, with the bottom side of the bung plug, the ring flange and the adapter ring forming a cage that receives the automatic venting device.
 19. The screw cap of claim 18, wherein the valve disk and the resilient element are inserted in the cage so as to be freely movable therein.
 20. The screw cap of claim 18, wherein a top side of the valve disk is elastically supported against the bung plug, wherein the adapter ring comprises an inwardly projecting radial flange ring, and wherein distal ends of the spring legs of the resilient element are elastically supported by the radial flange ring.
 21. The screw cap of claim 12, wherein an outside surface of the bung plug is covered with a cover to prevent incursion of water.
 22. The screw cap of claim 21, wherein the cover comprises an authentication seal.
 23. The screw cap of claim 12, further comprising a cover having a plurality of through openings for passage of air disposed on an outside surface of the bung plug, and a cap placed over the cover to prevent incursion of water.
 24. The screw cap of claim 12, wherein the container is an inner container of a pallet container. 